The basic theory and main features of operating modal analysis method have been elaborated, and then by using this method, the parameters of low-order natural characteristics of some wheeled and tracked self-propelled guns have been obtained. By two examples, the application of the operating modal analysis method for the development of self-propelled gun has been introduced. According to the result of operating modal analysis, for some wheeled self-propelled gun, "beat vibration" between the first-order natural characteristics and firing frequency of the gun has been identified, and further research indicates that the primary cause of the "beat vibration" is that the stiffness of the cradle is too weak which enlarges the vibratory response of the muzzle. With the reinforcement of the cradle, the testing result of firing indicates that the vibratory response of the muzzle is reduced obviously, and that the firing dispersion is much better than before. In order to certificate the accuracy of its dynamic model, for some tracked self-propelled guns, the natural characteristics of the whole gun through a comparison of the operating modal analysis and finite element calculation have been specified, and then according to the results of operating modal analysis, the dynamic model of the gun has been meliorated, and the natural characteristics of the gun by the finite element calculation are consistent with those by the operating modal analysis. This indicates that the model of the gun is correct with the vibratory response of the whole gun under seven running fire simulated, and that the error of vibratory response of the muzzle between firing testing and analog simulation does not exceed 15 %.